Comprehensive and Detailed Explanation:
Full duplex modeallows devices tosend and receive data simultaneously, improving network performance andreducing congestion, which iscritical for VoIP and video conferencing.
Breakdown of Options:
* A. A VLAN with 100Mbps speed limits- VLANssegment trafficbutlimiting speedsto100Mbpswould worsenvideo performance.
* B. An IP helper to direct VoIP traffic-IP helperis used forDHCP relay,notfor VoIP optimization.
* C. A smaller subnet mask- A smaller subnet reducesIP address availabilitybut doesnot improve network performance.
* D. Full duplex on all user ports-Correct answer.Full duplex eliminates collisions, allowingbetter VoIP and video performance.